But Mr Farage insisted there would not be a border between the republic and the British territory, as the UK “is not a third world country”.
The Brexit Party leader appeared on LBC radio where a called asked him if he thought his stance on Brexit threatened to bring problems to the region.
The former UKIP leader said: “When it comes to the peace argument - there is not going to be a hard border in Northern Ireland. There is not going to be soldiers and checkpoints - it isn't happening.
“The only difference is that if we left on WTO terms, there would be some tariffs to pay.
“Of course, we'd be logged in by lorry drivers on their mobile phones and the idea we'd have to stop goods coming in to the republic to ensure they weren't substandard - the UK is not a third world country.
“We would both start with parallel regulations. What does worry me slightly is that if there was a border poll, then that would be a genuine risk to peace.
“And I am a little bit concerned about that.”
Also during his LBC show, Mr Farage highlighted a fundamental part of the Prime Minister Boris Johnson’s speech in Wales.
The Brexit Party head pointed out the newly-appointed Tory leader said the UK would leave the single market and the customs union "in the next couple of years".
He described the comments as “the first watering down” of Mr Johnson’s “do or die” Brexit commitment.